How Fuel Injectors Work

Fuel injection allows an engine control computer to accurately measure how much fuel enters each individual cylinder, as opposed to controlling how much rich air enters all cylinders. It also can be scaled back for better fuel economy, or inject more for power, or skipped altogether for cylinder deactivation.

Fuel injected vehicles have been around for the past 3 decades, largely replacing carburetor fuel injection. Fuel is injected into the air stream leading up to the cylinder (or in the cylinder itself) as opposed to being mixed in the barrel style carburetor upstream, and then getting sucked in as a air/fuel mixture.

Today there are two types of fuel injection: port injected and direct injected engines. Port injection engines situate the fuel injector in the air intake so it mixes with the incoming air stream before the cylinder head valves. The rich air stream is then sucked into the combustion chamber and is controlled by the intake valve. Direct injection engines situate the fuel injector inside the cylinder head itself, pointing into the combustion chamber. This allows fuel to mix inside the cylinder on its expansion and compression stroke. In this video, a port injected engine is taken apart and the fuel system is examined, from the fuel rail, to the injectors, head and combustion chamber. A fuel injector is cut apart and examined, demonstrating the coil, plug connector, as well as the pintle valve and spray head. The advantages of direct injection vs port injection are discussed, which includes better emissions, fuel economy and mixing. A demonstration on carbon buildup is also presented, with many modern engines offering both port and fuel injected engines to mitigate this issue, such as in Toyota's D4S system.